1 files changed, 41 insertions, 13 deletions
diff --git a/libgo/go/runtime/chan.go b/libgo/go/runtime/chan.go
index 1b20aff..7878a8f 100644
--- a/libgo/go/runtime/chan.go
+++ b/libgo/go/runtime/chan.go
@@ -232,8 +232,7 @@ func chansend(c *hchan, ep unsafe.Pointer, block bool, callerpc uintptr) bool {
 		// Space is available in the channel buffer. Enqueue the element to send.
 		qp := chanbuf(c, c.sendx)
 		if raceenabled {
-			raceacquire(qp)
-			racerelease(qp)
+			racenotify(c, c.sendx, nil)
 		}
 		typedmemmove(c.elemtype, qp, ep)
 		c.sendx++
@@ -315,11 +314,8 @@ func send(c *hchan, sg *sudog, ep unsafe.Pointer, unlockf func(), skip int) {
 			// Pretend we go through the buffer, even though
 			// we copy directly. Note that we need to increment
 			// the head/tail locations only when raceenabled.
-			qp := chanbuf(c, c.recvx)
-			raceacquire(qp)
-			racerelease(qp)
-			raceacquireg(sg.g, qp)
-			racereleaseg(sg.g, qp)
+			racenotify(c, c.recvx, nil)
+			racenotify(c, c.recvx, sg)
 			c.recvx++
 			if c.recvx == c.dataqsiz {
 				c.recvx = 0
@@ -557,8 +553,7 @@ func chanrecv(c *hchan, ep unsafe.Pointer, block bool) (selected, received bool)
 		// Receive directly from queue
 		qp := chanbuf(c, c.recvx)
 		if raceenabled {
-			raceacquire(qp)
-			racerelease(qp)
+			racenotify(c, c.recvx, nil)
 		}
 		if ep != nil {
 			typedmemmove(c.elemtype, ep, qp)
@@ -647,10 +642,8 @@ func recv(c *hchan, sg *sudog, ep unsafe.Pointer, unlockf func(), skip int) {
 		// queue is full, those are both the same slot.
 		qp := chanbuf(c, c.recvx)
 		if raceenabled {
-			raceacquire(qp)
-			racerelease(qp)
-			raceacquireg(sg.g, qp)
-			racereleaseg(sg.g, qp)
+			racenotify(c, c.recvx, nil)
+			racenotify(c, c.recvx, sg)
 		}
 		// copy data from queue to receiver
 		if ep != nil {
@@ -861,3 +854,38 @@ func racesync(c *hchan, sg *sudog) {
 	racereleaseg(sg.g, chanbuf(c, 0))
 	raceacquire(chanbuf(c, 0))
 }
+
+// Notify the race detector of a send or receive involving buffer entry idx
+// and a channel c or its communicating partner sg.
+// This function handles the special case of c.elemsize==0.
+func racenotify(c *hchan, idx uint, sg *sudog) {
+	// We could have passed the unsafe.Pointer corresponding to entry idx
+	// instead of idx itself.  However, in a future version of this function,
+	// we can use idx to better handle the case of elemsize==0.
+	// A future improvement to the detector is to call TSan with c and idx:
+	// this way, Go will continue to not allocating buffer entries for channels
+	// of elemsize==0, yet the race detector can be made to handle multiple
+	// sync objects underneath the hood (one sync object per idx)
+	qp := chanbuf(c, idx)
+	// When elemsize==0, we don't allocate a full buffer for the channel.
+	// Instead of individual buffer entries, the race detector uses the
+	// c.buf as the only buffer entry.  This simplification prevents us from
+	// following the memory model's happens-before rules (rules that are
+	// implemented in racereleaseacquire).  Instead, we accumulate happens-before
+	// information in the synchronization object associated with c.buf.
+	if c.elemsize == 0 {
+		if sg == nil {
+			raceacquire(qp)
+			racerelease(qp)
+		} else {
+			raceacquireg(sg.g, qp)
+			racereleaseg(sg.g, qp)
+		}
+	} else {
+		if sg == nil {
+			racereleaseacquire(qp)
+		} else {
+			racereleaseacquireg(sg.g, qp)
+		}
+	}
+}